An increasing quantity of information is being exchanged today between computers (e.g. personal computers) by terminal users. The transfer of straightforward text in the form of electronic mail has traditionally played a leading role in this connection. But nowadays other forms of information including fax, audio, pictorial and video information as well as other types of computer data such as programs, data from databanks, measurement data and much more are being exchanged between computers. In view of this, the term "electronic mail" is used below to denote the exchange of data in any form between computers.
A disadvantage is that, in contrast with fax or telephone communications, the delivery of electronic mail directly to the user of a terminal device (e.g. the user of a PC on the Internet) requires substantial resources. Direct and automatic data transfer between a sending terminal device and a receiving terminal device is very complex as both terminal devices, or a central computer acting as an intermediate store, must be switched on and certain programs must be running on the computers to control the data exchange.
For security reasons (e.g. data security, security against system failure), central computers are thus generally unable to perform any other tasks and they must run day and night. Such "round-the-clock" systems are nowadays used mainly at an internal level by companies between their data processing networks at different locations (so-called routers or mail servers). They are also used today for connecting terminal devices to worldwide networks such as the Internet.
Users of electronic mail are nowadays dependent on so-called service providers, for example, who provide "round-the-clock" relay stations for electronic mail transmission.
In the processes proposed hitherto, electronic mail is sent via a "sender post office" and a worldwide network of intermediate computer terminals to a "recipient post office". In contrast with the terminal device of the actual recipient, this "recipient post office" is always on-line. Furthermore, the post offices cannot be directly controlled by the terminal users. The electronic mail remains at the recipient post office until the recipient, who is sitting at a terminal device, collects it. In this respect, the recipient must either regularly inquire at the post office or initiate measures himself. Although the actual transmission of electronic mail is completed within mere seconds, urgent mail cannot be sent in this way at the present time because the sender does not know if and when the actual recipient will collect the mail.
Furthermore, the intermediate post offices are frequently overloaded due to the ever-increasing quantities of data. As a result, data transfer can often only occur with immeasurable delays. Taking into consideration such delays, uncertain receipt of mail by the recipient and poor data protection on the Internet, the merits of the rapidity of electronic mail is put into perspective.
Hitherto, terminal users have thus been unable to avail themselves of a fully automatic, straightforward, direct, reliable and secure system of data transfer between a sending terminal device and a receiving terminal device, akin to that which exists in the case of telephone and fax communications.
For example, a fax can nowadays be sent over a telephone line directly to a recipient within a very short space of time, and be printed without any assistance from that recipient. Furthermore, the sender receives a confirmation that the fax has been correctly received by the recipient. The processes for electronic mail transmission proposed hitherto do not have these merits. This is a further reason why the fax retains its significance, although the transmission thereof is in principle slower than the transmission of electronic mail.
In the case of both telephone calls and faxes, data are transferred directly from a terminal user on the sending side to a terminal user on the receiving side, whereby neither the sender nor the recipient requires the services of a third party.
In EP 0 671 831 A1 there is considered an installation for receiving data which is to be forwarded to a terminal device, such as a data processing or data conversion device. If data is input when the terminal is switched off, the installation switches on the terminal device by means of a control signal. The data is temporarily stored at least until the terminal device is on-line. A disadvantage here is that the installation only works in regard to the terminal devices being put on line. Further, the disadvantages of existing electronic mail transmission are not overcome by this installation.
The article "Entlastung des zentralen Rechners durch frei programmierbare Nachrichtenubertragungssteuerungen?" (burotechnik, Automation+Organisation, November 1972, pages 1348-1356) describes a central computer to which user terminals are connected over telephone lines. Between the central computer and the terminals there is a control unit which is used to unburden the central computer. The control unit is described as the "front-end" for the central computer (back-end).
With the system described there is the drawback that an end user is entirely dependent on the central computer over which he has no influence. If, for example, a central computer goes down then all connected end users can neither send nor receive data via their data stations. Furthermore, there is an increased expense each time for the end user to log on to the central computer in order to read the data intended for him through his data station. The most serious disadvantage however is the fact that the end user receives no notification at a data station if certain data has come in for him while his data station or central computer is switched off or is not ready for operation.
From the publication "Electronic Mailbox" in Electronics & Wireless World Vol.91, No. 1594, August 1985, Surrey, pages 33-38, an apparatus and process are described for the direct electronic data transfer between two end appliances. Microcomputer systems are thereby used which are associated with the end appliances wherein the microcomputer systems can temporarily store incoming data irrespective of the operating state of the end appliances. Apart from a direct data transfer between two end appliances, no measures or devices are described by which the security of the data transfer or that of the end appliances could be increased.
WO A 93/20647 relates to a microcomputer system which is connected between a data line and an end appliance. More particularly, this microcomputer system is to temporarily store incoming and outgoing data and to carry out a conversion between different data formats. No special safety features can be drawn from this printed specification either.
U.S. Pat. No. 5,379,340 relates to a communications system wherein incoming data is checked at a terminal to see whether it has been fully transferred. A log file is thereby set up to serve as a type of certificate of receipt for the data received. Furthermore, the teaching of this specification contains no means for increasing the data security.